Email Remail/Resending instead of Forwarding
A plain message forward, as cPanel currenly uses for forwarding emails, simply redirects the email without changing any email headers. This often results in the email being flagged by anti-spam filters (including Gmail). Often this is because the sending IP doesn't match the sending domain's SPF records (for obvious reasons).
Remailing or resending would solve this problem, as the email would then be sent from an account on the cPanel server, with a reply-to address of the original sender, allowing it through spam filters and the emails would pass SPF checking.
cPanel should implement remailing in place of plain message forwarding, or at the very least in addition to forwarding, so that forwarded emails are less likely to be marked as spam at their final destination.